In a transmission electron microscope, observation with a low magnification and a bird's eye observation are frequently used for selecting a visual field area to be observed with a high magnification. A method of performing high-magnification display of the visual field area selected by the observation with the low magnification to observe a fine structure is also used frequently.
In general, observation with a low magnification and observation with a high magnification are switched by (1) changing a magnification rate of an observation object by using an image forming lens system, or (2) by preparing plural detectors in which distances between the image forming lens system and detectors differ and by switching the detectors used for observation as shown in Non-Patent Literature 1.
Moreover, a method of simultaneously performing observation with a low magnification and observation with a high magnification by periodically changing the magnification rate of the image forming lens system to synchronize the change with a signal output cycle of a display device is also proposed as shown in Patent Literature 1.